Design as applied to a helmet



FIG. 1 is a rear perspective view of the design as applied to a helmet showing my design;

FIG. 2 is a front perspective view thereof; and,

FIG. 3 is a bottom view thereof.

The broken line showing a helmet is for environmental purposes only and form no part of the claimed design. 

The ornamental design for a design as applied to a helmet, as shown and described. 